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q Controlling Rhizoctonia Diseases on Ornamentals with Fungicides
A.R. Chase and T.A. Mellich 1
University of Florida, IFAS, 3
Central Florida Research and Education Center Al~0 ka
CFREC-Apopka Research Report, RH-92-8 ida
Fungicides have continued to be an integral part of preventative control of R toctonia
diseases on most ornamental crops. New fungicides whose activity ranges iae not currently
known continue to become available for testing on ornamental crops. In addition, tests designed
to expand labels of registered fungicides are part of the CFREC-Apopka fungicide research
program. The diseases caused by Rhizoctonia solani which were included in 1991 and 1992
tests were foot rot and petiole blight of pothos, damping-off of spathiphyllum and china doll
seedlings, stem rot of vinca, leaf and stem rot of Liatris sp. and aerial blight of Boston fern.
Materials and Methods
Four tests were conducted with drench applications of pentachloronitrobenzene
formulations (PCNB Terraclor 75WP at 4 and 8 oz per 100 gal and Terraclor 4F at 6, 12 and
24 oz per 100 gal), and triflumizole (Terraguard 50WP at 4 and 8 oz per 100 gal). These tests
also included water sprayed inoculated and noninoculated controls. In addition, one test included
benomyl (Benlate 50WP at 16 oz per 100 gal) and another test included the combination product
of thiophanate methyl and mancozeb (Zyban 75WP at 24 oz per 100 gal). In the China doll
(Radermachera sinica) test, treatments were applied on 9 January 1992. In the spathiphyllum
(Spathiphyllum 'Gretchen') test, treatments were applied 6, 12, and 26 November 1991. In the
pothos (Epipremnum aureum) test, treatments were applied 22 August and 5 September 1991.
In the vinca (Catharanthus roseus) test, treatments were applied 19 September and 3 October
1991. Liatris sp. were treated on 11 and 25 March 1991. China doll plants were inoculated
with R. solani AG4 (87-265) on 10 January and the percentage of damped-off seedlings was
recorded on 17 January 1992. Spathiphyllum plants were inoculated with R. solani AG4 (87-
268) on 7 February and the number of dead leaves per plant was recorded on 4 March 1992.
Pothos plants were inoculated with R. solani AG4 (84-12) on 26 August and the number of dead
leaves per plant was recorded on 10 September 1991. Vinca plants were inoculated with R.
solani (89-151) on 23 September and the number of dead leaves per plant was recorded on 11
October 1991. Liatris were inoculated with R. solani (89-113) on 9 March and plant height and
severity of symptoms on the foliage were recorded on 30 March 1992.
The final test was performed with Boston fern (Nephrolepis exaltata). Treatments
included water sprayed controls (noninoculated and inoculated), chlorothalonil (Daconil 2787
90WDG at 20 oz per 100 gal), captain (Captan 50WP at 24 oz per 100 gal), benomyl (Benlate
50WP at 16 oz per 100 gal), mancozeb (Manzate 200 80WP at 24 oz per 100 gal), the
'Professor of Plant Pathology and Biological Scientist, respectively. Central Florida Research
and Education Center Apopka, 2807 Binion Road, Apopka, FL 32703.
combination product of thiophanate methyl and mancozeb (Zyban 75WP at 24 oz per 100 gal),
and three rates of a quaternary ammonium product (Greenshield at 1, 2, and 4 oz per 100 gal).
All treatments except for Greenshield were applied on 16, 23, and 30 September 1991.
Greenshield treatments were applied daily from 16 September to 6 October 1991. Boston ferns
were inoculated with R. solani AG4 (84-12) on 16 September and the percentage of the foliage
with aerial blight symptoms was recorded on 7 October 1991.
Results and Discussion
Excellent control of damping-off of china doll was achieved with all of the rates and
formulations of Terraclor and with both rates of Terraguard (Table 1). The same treatments did
not provide as high a degree of control of damping-off on spathiphyllum. In this test, best
control was achieved with the lower rates of Terraclor and both rates of Terraguard. The higher
rates of Terraclor formulations were associated with a slightly higher level of disease which may
have been due to a slight phytotoxicity reaction (Table 1). Zyban was employed in the pothos
test and provided excellent control of petiole rot as did all of the Terraclor and Terraguard
treatments (Table 1). Control of Rhizoctonia stem rot on vinca was best with Benlate 50WP,
but also was excellent with Terraguard (Table 1). The higher rates of Terraclor 75WP and 4F
gave very good disease control. Rhizoctonia leaf and stem rot of Liatris sp. was effectively
controlled with all fungicides tested with the lower rate of Terraguard (4 oz per 100 gal) and the
intermediate rate of Terraclor 4F (12 oz per 100 gal) being least effective (Fig. 1). The height
of the inoculated control plants was only about half that of the noninoculated control plants and
all of the fungicide treated plants. This indicates that even though disease control was not as
high with some of the fungicides, the plant achieved a normal height in the test period.
The final test for control of Rhizoctonia aerial blight of Boston fern showed excellent
control with Daconil 2787, Benlate 50WP, and Zyban and good control with Captan (Fig. 2).
Manzate and Greenshield did not provide as high a degree of control and Greenshield caused
severe foliar burning and especially at the 4 oz per 100 gal rate (Fig. 2).
Both formulations of Terraclor provided good control of these Rhizoctonia diseases of
ornamentals. The higher rates proved beneficial on some plants but may have resulted in slight
phytotoxicity on spathiphyllum. No discernible differences between the two formulations were
noted. Terraguard is now labelled for Cylindrocladium root and petiole rot of spathiphyllum.
These tests show that it is also an excellent choice for Rhizoctonia control with the 4 oz per 100
gal rate as effective as the higher rate. Daconil has been shown effective in controlling aerial
blight of Boston fern in the past. These tests also showed that Zyban could give a very high
degree of control when used on Boston fern. Zyban is a combination of the active ingredient
in Manzate (mancozeb) and thiophanate methyl (active ingredient in Cleary's 3336, Domain, and
Systec). Since Manzate did not give a high degree of control, the active portion in Zyban is
probably the thiophanate methyl. Further tests with thiophanate methyl compounds are planned.
Effect of Terraclor 75WP, Terraclor 4F, Terraguard 50WP, Zyban 75 %WP and Benlate 50WP
on severity of Rhizoctonia diseases of four ornamentals.
oz per China doll Spathiphyllum 'Pothos Vinca
Treatment" 100 gal % d.o.b no. dead leaves' no. dead leaves' no. dead leaves*
Noninoculated --- 0 a 0.4 ab 0 a 0 a
Inoculated -- 88.8 b 2.7 d 5.9 b 10.8 d
Terraclor 75WP 4 1.7 a 1.7 abcd 0 a 6.4 c
Terraclor 75WP 8 0.2 a 2.2 cd 0 a 2.3 ab
Terraclor 4F 6 0.2 a 1.8 bcd 1.0 a 5.0 be
Terraclor 4F 12 0.4 a 2.8 d 0.1 a 2.1 ab
Terraclor 4F 24 0 a 1.6 abcd 0 a nt'
Terraguard 50WP 4 1.6 a 1.2 abc 0.6 a 0.8 a
Terraguard 50WP 8 0.8 a 0.3 a 0 a 1.0 a
Zyban 75WP 24 nt nt 1.0 a nt
Benlate 50WP 16 nt nt nt 0 a
'In the china doll test, treatments were applied on 9 January 1992. In the spathiphyllum test, treatments were
applied 6, 12, and 26 February 1992. In the pothos, treatments were applied 22 August, and 5 September
1991. In the vinca test, treatments were applied 19 September and 3 October 1991.
bChina doll plants were inoculated on 10 January and the percentage of plants that damped-off (d.o.) was
recorded on 17 January 1992.
"Spathiphyllum plants were inoculated on 7 February and the number of dead leaves per plant was recorded
on 4 March 1992.
dPothos plants were inoculated on 26 August and the number of dead leaves per plant was recorded on 10
'Vinca plants were inoculated on 23 September and the number of dead leaves per plant was recorded on 11
tMeans in the same column followed by a different letter were statistically different (DNMRT, P = 0.05).
Figure 1. Effect of various fungicides on severity of Rhizoctonia leaf and stem rot of Liatris sp. caused
by R. solani. Disease was rated on the following scale: 0 = no symptoms, 1 = slight, 2 =
moderate, 3 = high, and 4 = dead.
Noninoc Inoc TcIr-W TcIr-W Tclr-F TIcr-F Tclr-F Terr
ulated ulated 4 oz 8 oz 6 oz 12 oz 24 oz 4 oz
Terr 66825 66825
8 oz 4 oz 16 oz
Figure 2. Effect of various fungicides on severity of Rhizoctonia aerial blight of Boston fern (Nephrolepis
exaltata) caused by R. solani.
Noninoc Inoc Daconil Captan Benlate Manz Zyban
ulated ulated 20 oz 24 oz 16 oz 24 oz 24 oz
Grsh Grsh Grsh
1 oz 2 oz 4 oz